From: Catalin Marinas <catalin.marinas@arm.com>
To: Peter Collingbourne <pcc@google.com>
Cc: andreyknvl@gmail.com, linux-mm@kvack.org,
kasan-dev@googlegroups.com, ryabinin.a.a@gmail.com,
linux-arm-kernel@lists.infradead.org, vincenzo.frascino@arm.com,
will@kernel.org, eugenis@google.com
Subject: Re: [PATCH] kasan: call clear_page with a match-all tag instead of changing page tag
Date: Thu, 16 Feb 2023 14:27:47 +0000 [thread overview]
Message-ID: <Y+49Y4lD4GmDP8fc@arm.com> (raw)
In-Reply-To: <20230216064726.2724268-1-pcc@google.com>
On Wed, Feb 15, 2023 at 10:47:26PM -0800, Peter Collingbourne wrote:
> Instead of changing the page's tag solely in order to obtain a pointer
> with a match-all tag and then changing it back again, just convert the
> pointer that we get from kmap_atomic() into one with a match-all tag
> before passing it to clear_page().
>
> On a certain microarchitecture, this has been observed to cause a
> measurable improvement in microbenchmark performance, presumably as a
> result of being able to avoid the atomic operations on the page tag.
Yeah, this would likely break the write streaming mode on some ARM CPUs.
> Signed-off-by: Peter Collingbourne <pcc@google.com>
> Link: https://linux-review.googlesource.com/id/I0249822cc29097ca7a04ad48e8eb14871f80e711
> ---
> include/linux/highmem.h | 8 +++-----
> 1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/highmem.h b/include/linux/highmem.h
> index 44242268f53b..bbfa546dd602 100644
> --- a/include/linux/highmem.h
> +++ b/include/linux/highmem.h
> @@ -245,12 +245,10 @@ static inline void clear_highpage(struct page *page)
>
> static inline void clear_highpage_kasan_tagged(struct page *page)
> {
> - u8 tag;
> + void *kaddr = kmap_atomic(page);
>
> - tag = page_kasan_tag(page);
> - page_kasan_tag_reset(page);
> - clear_highpage(page);
> - page_kasan_tag_set(page, tag);
> + clear_page(kasan_reset_tag(kaddr));
> + kunmap_atomic(kaddr);
> }
Please don't add kmap_atomic() back. See commit d2c20e51e396
("mm/highmem: remove deprecated kmap_atomic"). I'd duplicate the
clear_highpage() logic in here and call clear_page() directly on the
address with the kasan tag reset.
--
Catalin
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2023-02-16 14:29 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-16 6:47 [PATCH] kasan: call clear_page with a match-all tag instead of changing page tag Peter Collingbourne
2023-02-16 14:27 ` Catalin Marinas [this message]
2023-02-16 20:04 ` Peter Collingbourne
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=Y+49Y4lD4GmDP8fc@arm.com \
--to=catalin.marinas@arm.com \
--cc=andreyknvl@gmail.com \
--cc=eugenis@google.com \
--cc=kasan-dev@googlegroups.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-mm@kvack.org \
--cc=pcc@google.com \
--cc=ryabinin.a.a@gmail.com \
--cc=vincenzo.frascino@arm.com \
--cc=will@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).